The invention relates to a plasma picture screen provided with a front plate which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate carrying a phosphor layer, with a ribbed structure which divides the space between the front plate and the carrier plate into plasma cells filled with a gas, and with one or more electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells.
Plasma picture screens render possible color images with high resolution and large screen diagonals and are of a compact construction. A plasma picture screen has a hermetically sealed glass cell filled with a gas, with electrodes in a grid arrangement. The application of a voltage triggers a gas discharge which generates light in the ultraviolet range. This light can be converted into visible light by phosphors and emitted through the front plate of the glass cells to a viewer.
Additive color mixing is used for showing color images on a plasma picture screen. Many of the colors present in nature can be displayed by additive mixing of the three primary colors, red, green, and blue of suitable relative intensities.
The display of the different colors is established by so-called standard color curves. A commonly used standard is the CIE color triangle. The range of displayable colors in a screen is defined by the color dots of the three phosphors, given by the respective emission spectra.
Owing to the characteristic color sensitivity of the human eye, the blue light emission contributes least to the luminance (brightness) of a screen. In addition, the blue-emitting phosphor is not as efficient as the green- and red-emitting phosphors in plasma picture screens. A plasma picture screen with a blue-emitting phosphor is known, for example, from DE 199 37 420. These two effects lead to the color temperature for white light for television applications, given an equal excitation of red-, green-, and blue-emitting phosphors, being lower than desired.
It is accordingly an object of the invention to avoid the disadvantages of the state of the art and to provide a plasma picture screen with an improved color temperature for white light.
This object is achieved by a plasma picture screen provided with a front plate which comprises a glass plate on which a dielectric layer and a protective layer are provided, with a carrier plate carrying a phosphor layer, with a ribbed structure which divides the space between the front plate and the carrier plate into plasma cells filled with a gas, and with one or more electrode arrays on the front plate and the carrier plate for generating corona discharges in the plasma cells, wherein the front plate has a blue layer on its side facing the plasma cells.
The blue layer achieves a blue coloration of the front plate, and hence the white color point of the plasma picture screen is shifted towards lower x,y values. The color temperature of the plasma picture screen is also raised by this coloration of the front plate.
In an advantageous embodiment, the blue layer is the protective layer. This has the advantage that no additional protective layer, for example of MgO, need be applied to the front plate.
In this advantageous embodiment, it may be preferred for the blue layer to be structured and to be parallel to the electrodes on the front plate. The addressing behavior of the plasma picture screen can be improved by this measure.
The blue layer can be produced in a simple manner by the application of blue colorant particles in the dielectric layer.
It may be advantageous for the blue layer to be applied as an additional layer on the glass plate and on the electrodes of the front plate.
It is particularly preferred if the blue layer contains colorant particles selected from the group comprising CoAl2O4 and blue ultramarines.
The inorganic pigments are temperature-stable and resist rigid conditions in the manufacture and operation of a plasma picture screen. In particular, blue layers which contain CoAl2O4 are resistant to the ion stream generated in a plasma discharge. Furthermore, CoAl2O4 has a high secondary electron coefficient under ion bombardment.